Oral cleansing product

ABSTRACT

There is disclosed an oral cleansing product comprising as an abrasive an alumnina in the form of particles having d 10  below 3.5 μm, d 50  below 1.0 μm, and a specific surface area below 6 m 2 /g.

International standard ISO11609 of 1995 contains the followingdefinitions:

Dentifrice: any substance or combination of substances speciallyprepared for the public for cleaning the accessible surfaces of teeth.

Toothpaste: any semi-solid dentifrice preparation presented in the formof a paste, cream or gel.

This invention is concerned with oral cleansing products, includingdentifrices and (to the extent that they are not classed as dentifrices)chewing gum and candy.

An oral cleansing product invariably contains an abrasive powder forcleaning purposes. The cleaning and abrasive properties of the oralcleansing product depend on the concentration of the powder, on theMoh's hardness of the abrasive, and on the shape and particle size andsize distribution of the powder. The cleaning effect of an oralcleansing product concerns its effectiveness in removing adventitiousstains and other deposits from the surface of teeth and other parts oforal cavity. The abrasive effect or abrasivity concerns undesiredremoval of surface components of teeth including enamel and dentine, andundesired damage in the oral cavity. An oral cleansing product having ahigh cleaning effect generally has a rather high abrasivity, and viceversa. ISO11609 provides methods for testing abrasivity and sets limitson dentifrices marketed in Europe. An earlier British standard BS5136 of1981 also sets limits on abrasivity by comparison with a standardreference toothpaste, which is also used as a reference in ISO11609, andwhich has the formulation:

Precipitated calcium carbonate 40% w/w.

Glycol 25% w/w

Sodium carboxymethylcellulose 1.40% w/w

Dodecyl sodium sulphate 1.00% w/w

Sodium silicate (80° TW of approximately pH 7) 0.05% w/w

Saccharin sodium 0.15% w/w

Formalin (40% (m/m) formaldehyde) 0.10 w/w

Peppermint flavouring 0.80% w/w

Water 33.05% w/w

Abrasive powders used or contemplated for use in oral cleansing productsinclude silicas, including gels and precipitates, sodium bicarbonate,calcium and magnesium carbonates, calcium phosphates, alumina andhydrates thereof, aluminosilicates, aluminium and magnesium silicates,and thermosetting urea-formaldehyde and other plastics materials. Thereis a need in the industry for an abrasive for inclusion in oralcleansing products, which provides good cleaning properties, inparticular stain removal, while showing relatively low abrasivity. Inparticular, there is a need for an abrasive which can be incorporated ina concentration large enough to provide an excellent cleaning effectwith low abrasivity which nevertheless complies with the abrasivityrequirements of the above-stated standard specifications. This inventionaddresses that need.

U.S. Pat. No. 3,957,968 teaches the use of flat flakes of α-aluminiumoxide in toothpaste. The flakes have a median particle size of 2 to 7μm. U.S. Pat. No. 4,060,599 discloses the use of a finer aluminium oxide(median 1 to 2 μm) and specifically uses Reynolds RC152DBM which has amedian size of around 1.7 μm.

U.S. Pat. No. 4,632,826 teaches the use of a weakly calcined aluminapolishing agent. This polishing agent consists of 10% to 50% by weight γaluminium oxide and 50% to 90% by weight α aluminium oxide.

GB-A-2155333 teaches the use of calcium hydrogenphosphate anhydride andan aluminium oxide having an average particle size of 0.5 μm to 10 μm.The alumina has a high a-content, as measured by X-ray diffraction.

WO-A-95/33441 teaches the use of cationically charged colloids of ametal compound. The colloid has a particle size of 0.001 μm to 0.2 μm.

GB-A-2037162 and GB-A-2009596 disclose the use of hydrated aluminas indentifrice products.

The phrase “alumina” is sometimes loosely used to cover a number ofaluminium oxide, oxide hydroxide and trihydroxide compounds. The correctdesignations and some crystalline phases are shown below:

Accepted Crystallographic and Mineral Name Chemical Composition ChemicalDesignation Gibbsite Aluminium trihydroxide γ - Al(OH)₃ BayeriteAluminium trihydroxide α - Al(OH)₃ Nordstrandite Aluminium trihydroxideAl(OH)₃ Boehmite Aluminium oxide hydroxide γ - AlOOH Diaspore Aluminiumoxide hydroxide α - AlOOH Corundum Aluminium oxide α - Al₂O₃

This invention is concerned with alumina that is essentially Corundum.Corundum is produced by calcination of aluminium trihydroxides and oxidehydroxides. Depending on the form of aluminium trihydroxide and oxidehydroxide starting material, a number of forms of alumina (oftendescribed as activated aluminas) are produced before corundum is formed.Another form of alumina chemical is aluminium hydroxide gel, which isoften formed by the neutralisation of an aluminium salt solution.

The invention provides an oral cleansing product comprising as anabrasive an alumina in the form of particles having d₁₀ below 3.5 μm,d₅₀ below 1.0 μm, and specific surface area below 6 m²/g.

According to a further aspect of the present invention, there isprovided the use of alumina as an abrasive in an oral cleansing product,wherein the alumina is in the form of particles having d₁₀ below 3.5 μm,d₅₀ below 1.0 μm, and a specific surface area below 6 m²/g.

According to a further aspect of the present invention, there isprovided the use of alumina as a whitening agent in an oral cleansingproduct, wherein the alumina is in the form of particles having d₁₀below 3.5 μm, d₅₀ below 1.0 μm, and a specific surface area below 6m²/g. In this way the alumina used may serve the purpose of replacingtitania or the like in conventional products, thus resulting in a costsaving.

The surface area is measured by the following method. A sample ofalumina of sufficient weight to give an estimated surface area of about0.5 to 25 m² is degassed in a Micrometrics Desorb 2300B at about 150° C.until a stable reading is obtained. The sample is then transferred to aMicrometrics Flowsorb II 2300, cooled and immersed in a mixture of 30% Nand 70% He gas. The total amount of N absorbed is measured from thechange in thermal conductivity of the gas mixture preferably duringdesorption as the temperature is raised again to room temperature.Surface area per gram is then calculated from the total gas absorbed andthe weight of the sample.

The particle size is measured as follows. Particle size distribution ofa sample of alumina is measured in a Sedigraph 5100 instrument supplied,by Micrometrics Products.

The abrasive is preferably an anhydrous alumina, generally a calcinedalumina or alternatively a tabular or fused alumina. Calcination iseffected at a temperature of at least 900° C. Higher calcinationtemperatures result in harder products. The alumina used in thisinvention is preferably fairly hard, such as may be obtained bycalcination at above 1000° C. The alumina in this invention is anα-alumina. Preferably, the α content is greater than 90%, preferablygreater than 93%, even more preferably greater than 95%, as measured byX-ray diffraction. In a preferred embodiment, the γ-content is less than1%.

The abrasive is used in the form of particles having d₁₀ below 3.5 μm,preferably below 2.5 μm. (d₁₀, d₅₀ and d₉₀ are used in conventionalmanner to indicate that 10, 50 or 90 wt % of the product has a particlesize above the stated value). Preferably, the alumina abrasive is asub-micron product, having d₅₀ of 0.1-1.0 μm. Preferably the aluminaabrasive has a relatively narrow particle size distribution, e.g. withd₁₀ being no greater than four times d₅₀.

The alumina abrasive has a specific surface area below 6 m²/g,preferably in the range of 4.5-5.0 m²/g. The specific surface area isrelated to the aforesaid parameters of hardness (harder products havelower specific surface areas) and particle size (more finely dividedproducts have larger specific surface areas).

Alumina products of the kind described are readily availablecommercially, for they are produced in substantial quantities mainly foruse in refractories and ceramics. Grinding may conveniently be effectedby fluid energy or vibratory milling (micronising) or preferably by ballmilling.

When an abrasive powder has excellent stain removal properties in onetoothpaste, it is generally the case that it will be found to haveexcellent stain removal properties in other oral cleansing products.Although the abrasivity of an oral cleansing product does depend to asignificant extent on the whole formulation, and not merely on thenature and concentration of the abrasive present in it, nevertheless anabrasive which shows high or low abrasivity in one formulation maygenerally be expected to show correspondingly high or low abrasivity inothers.

The alumina abrasive is preferably present in the oral cleansing productat a concentration of 1-15% w/w, preferably higher than 2%, even morepreferably higher than 3%, e.g. 3-12% w/w. Toothpastes and other oralcleansing products include a wide variety of components in a widevariety of concentrations. The alumina should be compatible with otheringredients. The following list is intended to be exemplary rather thandefinitive or restrictive.

Toothpastes are generally water-based. Other dentifrice formulations aretypically water-based or are supplied dry and require water foractivation. Chewing gums and candies are generally based on natural orsynthetic elastomers or gum bases.

A binder or thickener is generally present. Examples of suitablematerials are carboxyvinyl polymers, carrageenan, hydroxyethyl celluloseand water soluble salts of cellulose ethers such as sodiumcarboxymethylcellulose and sodium carboxymethyl hydroxyethyl cellulose.Natural gums and colloidal silica or silicate materials can also beused. Binders or thickeners are generally present in an amount fromabout 0.15 to about 5.0% w/w of the total composition.

A humectant is also generally used to keep the formulation fromhardening on exposure to air. Examples of suitable humectants areglycerine, sorbitol, xylitol, polyethylene glycols and propylene glycol.Humectants are generally present in an amount from about 10% to about70% w/w of the weight of the composition.

One or more particulate materials, regarded as abrasives or abrasivepolishers or fillers, are also present. The alumina abrasive describedabove is one such, but others may also be present as noted above.Examples are:

Silicas, including gels and precipitates, sodium bicarbonate, calciumand magnesium carbonates, dicalcium phosphate dihydrate, alumina andhydrates thereof, aluminosilicates, aluminium and magnesium silicates,and thermosetting urea-formaldehyde and other plastics materials. It ispreferred that the alumina is not present in combination with calciumhydrogenphosphate anhydride.

Abrasives are generally present at a level of about 10% to about 70%,preferably from about 15% to about 25%, w/w of the formulation.

A source of fluoride ion is preferably provided. Regulatory authoritiesin various countries may stipulate a maximum and/or a minimum totalfluoride ion concentration.

Chewing gums are generally based on one or more of: natural andsynthetic elastomers e.g. polybutene or polyisobutene, which may besoftened with vegetable fats or oils or plasticisers; waxes; humectantssuch as xylitol; natural and synthetic resins and gum bases such aschicle.

Other components which may also be included in oral cleansing productsin accordance with conventional practice, include sweeteners, flavours,colours, peroxides or other bleaching agents, anti-calculus agents,anti-plaque agents, anti-bacterial agents, preservatives andeffervescence generators.

Toothpaste and other oral cleansing products may be manufactured byconventional techniques. The alumina abrasives with which this inventionis concerned are rather easy to incorporate for, unlike some otherabrasive powders, they are generally not prone to lumping.

Here is an example of a toothpaste formulation:

Dicalcium phosphate 40% w/w

Alumina 10%

Sorbitol 25%

Polyethylene glycol 2%

Carboxymethylcellulose 1.1%

Sodium Saccharin 0.2%

Sodium Lauryl Sulphate 1.5%

Benzoic Acid 0.15%

Sodium Benzoate 0.2%

Water 19.5%

This formulation based on dicalcium phosphate polishing agent/filler,has been used to test the properties of various alumina abrasives. Inthe experimental section below, a different formulation based on asilica polishing agent/filler was used. Although the results obtainedwith the two formulations were different in absolute terms, they weregenerally the same in relative terms, i.e. any particular aluminaabrasive generally had the same or a similar effect on the properties ofboth formulations. This justifies the assertion that an abrasive showingvaluable properties in one toothpaste may reasonably be expected to showcorresponding valuable properties in other oral cleansing products.

The alumina abrasives used in the experimental section below are eithercommercial products or development products (designated BAX). availablefrom Alcan Chemicals Limited, and are here identified by means of theirtrade names. This invention is based on the discovery that thedevelopment product BAX842 has unexpectedly and outstandingly goodproperties.

EXAMPLE 1

In this example, a silica-based toothpaste was used. The formulation Wasas shown in Table 1.

TABLE 1 Silica-based toothpaste formulation Ingredient % w/wPolyethylene Glycol 3.0 Sodium carboxymethyl cellulose 0.6 DeionisedWater 7   Sodium Fluoride  0.243 10% Sorbitol 56.107 Sodium Saccharin0.3 Titanium Dioxide 0.3 Abrasive Silica 20.5  Flavour  0.75 SodiumLauryl Sulphate 1.2 Alumina 10.0  Total 100   

The alumina products used in this example are given in Table 2.

TABLE 2 Mineralogy/ SSA Sedigraph Product Milling route m²/g d₁₀ d₅₀ d₉₀X Alumina/micronised 1.3 5.19 3.11 1.4  RA207LS Alumina/ball milled 8.21.01 1.4  0.18 BAX888 Alumina/ball milled 6.8 1.41 0.48 0.27 BAX842Alumina/ball milled 4.8 2.35 0.62 0.36 BAX904 Alumina/ball milled 6.12.07 0.51 0.25 PA2 (1) Alumina/ball milled 6.7 8.24 1.18 0.47 PA2 (2)Alumina/micronised 4.4 6.83 0.99 0.51 MA250 Alumina/micronised 4.611.05  1.29 0.49 BAX 985A Alumina/ball milled 5.9 3.23 0.53 0.28 BAX985B Alumina/ball milled 6.6 2.47 0.49 0.25

For stain removal, samples were subjected to an in-vitro test developedand performed by the Health Science Research Centre at IndianaUniversity—Purdue University. This test involves staining teeth using abroth containing instant coffee, instant tea, gastric mucin3 and amicrococcus leteus culture. The colour of the stained teeth is measuredusing a Minolta colourmeter. The teeth are then brushed with thetoothpaste and the colour measured. A measurement of stain removal isthen calculated.

The enamel abrasivity (Designated REA) was measured by MissouriAnalytical Laboratories, using a method described by R J Grabenstetteret al. (J D Res. Vol. 37, November-December 1958, No. 6, pages 1060-8).

The abrasivity and stain removal results are shown in Table 3.

TABLE 3 Abrasivity and stain removal results Enamel Abrasivity StainRemoval REA Value % X 149  55 RA207LS 45 42 BAX888 53 42 BAX842 46 50BAX904 58 40 PA 2(1) 70 43 PA2 (2) 80 37 MA250(3) 110  54 BAX 985A 86 50BAX 985B 77 42

Discussion

The comparative performance of the aluminas in terms of abrasivity (REAvalue) and stain removal is shown in FIG. 1. BAX 842 is outstanding.

The relationship between particle size d₁₀ and enamel abrasivity isshown in FIG. 2. For the ball milled products, it can be seen in FIG. 2that there is a linear relationship (R²=0.96, equation y=18.985×+25.109)between REA value and d₁₀ with REA falling as the d₁₀ decreases. BAX842does not fit this linear relationship as the abrasivity is much lessthan would be expected for its d₁₀, i.e. for a d₁₀ value of 2.35 μm, thelinear regression equation calculates an enamel abrasivity of 69 versus46 obtained with BAX842. There is no relationship between enamelabrasivity and d₁₀ for the micronised aluminas. The relationship betweenstain removal and d₁₀ for the ball milled and micronised aluminas showssignificant scatter in performance with no linear relationship.

EXAMPLE 2

Sugar-free chewing gums to the formulations shown below were preparedusing the following method.

The sugar-free gum base was heated in an oven at 70-75° C. forapproximately 2 hrs until it softened. A Z-blade mixer was preheated to45° C. and the softened gum base was added. The mannitol powder wasadded in small doses and was mixed until well combined. 60% of the totalSorbitol powder was added in small doses until it was well combined.Where applicable, the alumina was added in small doses and again mixeduntil well combined. The lecithin was then added and mixed until wellcombined. A further 20% of the total Sorbitol powder was added in smalldoses and mixed until well combined. 50% of the total glycerine wasadded and mixed until well combined. A further 10% of the Sorbitolpowder was added until well combined. A remaining 50% of the glycerinewas added until well combined. The maltitol syrup was added in smalldoses until well combined. The remaining 10% of the total Sorbitolpowder was then added in small doses and mixed until well combined.During the mixing operation, the mixer temperature was maintained at 45°C.

The product was removed from the mixer and transferred to a marble slab,which had been pre-dusted with mannitol. The product was covered withgrease-proof paper dusted with mannitol powder and rolled by hand usinga pin roll until a uniform thickness of approximately 1 cm was achieved.The product was then passed through a mechanical sheeter whilstgradually reducing the depth until a thickness of approximately 2 mm wasobtained. Using roll cutters, the product was cut into stripsapproximately 1 cm wide. Using a knife, the strips were cut into 5 cmlengths. The gum was then wrapped in paper-lined foil and stored at20-25° C.

TABLE 4 Chewing gum formulations (Example 2) Control Gum 1 Gum 2 Gum 3Gum 4 Gum 5 Ingredient (%) (%) (%) (%) (%) (%) Gum base 28.95 28.9528.95 28.95 28.95 28.95 Sorbitol 50.10 40.10 40.10 45.10 47.10 49.10Maltitol syrup  8.15  8.15  8.15  8.15  8.15  8.15 Glycerine  7.15  7.15 7.15  7.15  7.15  7.15 Mannitol  5.15  5.15  5.15  5.15  5.15  5.15Lecithin 0.5 0.5 0.5 0.5 0.5 0.5 Alumina X — 10   — — — — BAX842 — —10   5   3   1  

Alumina Products Tested

The alumina products tested in this example are given in Table 5:

SSA Sedigraph psd (μm) Product Milling Route (m²/g) D10 D50 D90 BAX842Ball milled 4.8 2.3  0.62 0.36 X Micronised 1.3 5.19 3.11 1.4 

Observations

All the formulations gave final products with an homogeneous appearanceand a texture and consistency expected for typical chewing gum. Thealumina formulations were whiter than the control product. Also as thealumina addition level increased the gum became more manageable and lesssticky.

Stain Removal Performance

The stain removal performance of the chewing gum formulations wasmeasured at Indiana University—Purdue University. The test involvestreating stained teeth for 60 minutes with 5 g of chewing gum usingmechanical mastication; the gum is changed every 20 minutes. The colourof the teeth before and after chewing was measured using a MinoltaCM-5031 spectrophotometer. The overall change in stain (delta E value)is calculated from the CIE L*a*b*equation.

The results for the formulations are shown in Table 6:

Product Alumina Addition Level Delta E Value, % Control 0% 7.5 X 5% 9.6BAX842 1% 10.1  BAX842 3% 11.7  BAX842 5% 13.7  BAX842 10%  35.2 

The enamel abrasivity values for these aluminas in toothpaste is shownbelow.

Product Enamel Abrasivity, REA X 149 BAX842  46

It is surprising that BAX842 despite its finer particle size and lowerenamel abrasivity gave greater stain removal performance than alumina X.

EXAMPLE3

Sugar-free chewing gums to the formulations shown in Table 7 wereprepared in the same manner as described in Example 2. These experimentsused a different gum base and substituted 0.25% Sorbitol by peppermintflavouring. The characteristics of the aluminas used in theseexperiments are shown in Table 2 in Example 1.

TABLE 7 Chewing gum formulations (Example 3) Gum 1 Gum 2 Gum 3 Gum 4 Gum5 Ingredient (%) (%) (%) (%) (%) Gum base 28.95 28.95 28.95 28.95 28.95Sorbitol 39.85 39.85 39.85 39.85 39.85 Maltitol syrup  8.15  8.15  8.15 8.15  8.15 Glycerine  7.15  7.15  7.15  7.15  7.15 Mannitol  5.15  5.15 5.15  5.15  5.15 Lecithin 0.5 0.5 0.5 0.5 0.5 Peppermint flavour  0.25 0.25  0.25  0.25  0.25 Alumina Y 10   — — — — BAX842 — 10   — — —BAX888 — — 10   — — BAX985A — — — 10   — BAX904 — — — — 10  

As described in Example 2, the stain removal performance of the chewinggum was measured at Indiana University—Purdue University. The resultsare shown in Table 8.

TABLE 8 Stain removal results for chewing gum formulations (Example 3)Alumina X BAX842 BAX888 Blend 5 BAX904 Stain Removal 11.0 13.5 9.9 8.88.9 Performance, %

It is surprising that despite being significantly finer than alumina X,BAX842 gave a>20% increase in stain removal performance. Also, comparedwith other sub-micron alumina products (BAX888, BAX985A and BAX904)BAX842 gave a significantly higher stain removal performance.

What is claimed is:
 1. An oral cleansing product comprising as anabrasive in a formulation of the oral cleansing product an alumina inthe form of particles having d₁₀ below 3.5 μm, d₅₀ below 1.0 μm, and aspecific surface area below 6 m²/g, wherein the alumina is at least 90%α-alumina calcined at a temperature of at least 900° C.
 2. The oralcleansing product of claim 1 wherein d₁₀ is below 2.5 μm.
 3. The oralcleansing product of claim 1 wherein the specific surface area is4.5-5.0 m²/g.
 4. The oral cleansing product of claim 1, wherein theparticles have d₅₀ of 0.1-1.0 μm.
 5. The oral cleansing product of claim4, wherein the ratio of d₁₀ to d₅₀ is not more than 4.0.
 6. The oralcleansing product of claim 1, wherein the abrasive is present in aproportion of 1-15% w/w.
 7. The oral cleansing product of claim 1,wherein the alumina is ball-milled.
 8. The oral cleansing product ofclaim 1, wherein the alumina has an α content of greater than 90%. 9.The oral cleansing product of claim 8, wherein the alumina has an αcontent greater than 93%.
 10. The oral cleansing product of claim 1,which is a dentifrice.
 11. The oral cleansing product of claim 1, whichis a chewing gum.
 12. An oral cleansing method comprising cleaning partsof an oral cavity with an oral cleansing product containing alumina asan abrasive, wherein the alumina is in the form of particles having d₁₀below 3.5 μm, d₅₀ below 1.0 μm, and a specific surface area below 6m²/g, and wherein the alumina is at least 90% α-alumina calcined at atemperature of at least 900° C., such that he oral cleansing product iseffective in removing deposits from dental surfaces without undesiredremoval of dental surface components.
 13. An oral cleansing methodcomprising cleaning parts of an oral cavity with an oral cleansingproduct containing alumina as a whitening agent, wherein the alumina isin the form of particles having d₁₀ below 3.5 μm, d₅₀ below 1.0 μm, anda specific surface area below 6 m²/g, and wherein the alumina is atleast 90% α-alumina calcined at a temperature of at least 900° C., suchthat the oral cleansing product is effective in removing deposits fromdental surfaces without undesired removal of dental surface components.